1. Field of the Invention
The present invention relates to a method of inspecting a thin-film magnetic head, and a method of making a thin-film magnetic head.
2. Related Background Art
In general, a thin-film magnetic head mounted in a hard disk drive or the like comprises a magnetoresistive film having a free layer whose magnetization direction changes depending on an external magnetic field and a pair of hard bias layers (ferromagnetic layers) for applying a bias magnetic field to the free layer and thereby achieving a single domain of magnetization direction (e.g., Japanese Patent Application Laid-Open No. HEI 10-242544). Under the influence of an external magnetic field from a hard disk (recording medium) or the like, the magnetization direction of the free layer changes, whereby information recorded on the hard disk or the like is reproduced according to the ohmic value corresponding to the magnetization direction.
In such a thin-film magnetic head, the write width for recording a signal and the read width for reproducing the same have been narrowing in a accelerated fashion as the recording density of the hard disk becomes higher. Therefore, the thin-film magnetic head produced by various thin-film processes is hard to make, whereby defective products with inferior properties may sometimes occur.
In general, properties of a thin-film magnetic head have been inspected in the following manner. First, a wafer formed with a plurality of thin-film magnetic heads is diced, so as to yield a bar in which heads are arranged in a row. Subsequently, the thin-film magnetic heads are lapped on their side facing the hard disk, so as to yield a desirable MR height. Then, the bar in such a state is set to an inspection apparatus. The inspection apparatus comprises a table for mounting the bar, a constant-current power supply which supplies a sense current to the magnetoresistive film in each thin-film magnetic head, a magnetic field generator such as Helmholtz coil which applies an external magnetic field to the thin-film magnetic head, etc.
After the inspection apparatus is prepared, the magnetic field generator is actuated, so as to apply an external magnetic field to the thin-film magnetic heads in the bar while the constant-current power supply supplies a sense current to the thin-film magnetic heads. In this environment, QST (Quasi Static Test) for inspecting properties such as a reproducing output of the thin-film magnetic head or an asymmetric property of output amplitude with respect to changes in the external magnetic field (so-called asymmetry) was carried out. Further, property values obtained by the inspection are compared with their reference values, so as to determine whether individual thin-film magnetic heads are favorable or not, whereby those failed are prohibited from shipping, etc. Examples of literatures disclosing such a method of inspecting a thin-film magnetic head include Japanese Patent Application Laid-open No. 2000-260012 and Japanese Patent Application Laid-Open No. HEI 6-150264.